This invention relates to an improved method for continuous production of laminated sheet products and, more particularly, to a method for continuous production of laminated sheets which comprises transporting a plurality of continuous sheet component materials, drying or conditioning the same component materials if necessary, impregnating them with a curable resin composition, drying the same if necessary, joining the resin-impregnated component materials to give an assembly, laminating the assembly with a film material on either side, curing the resin and cutting the laminate to size or otherwise treating it.
The term "laminated sheet" as used throughout this specification and the claims appended thereto means such products as, in the main, electrical insulation sheets and copper foil laminates for printed circuit boards which are built into electrical appliances, electronic components and so on. Heretofore, such laminated sheets have been commercially produced batchwise, i.e. by impregnating a sheet material with a curable resin varnish, drying the varnished material, preparing prepregs corresponding to the specified size and pressing a plurality of the prepregs in superimposition under the influence of heat to provide a finished sheet product. However, this production method is procedurally complicated, requires a large production labor force, and is not as productive as might be desired. Thus, the industry needed a continuous, efficient production method. To overcome the disadvantages, several continuous processes have been proposed in recent years. In this regard, reference should be made to Japanese Unexamined Patent Publication Nos. 10390/1977, 88872/1978, 13572/1979, 4838/1980, etc.
These proposed methods for continuous production of a laminated sheet involve either one of the following processes.
(1) A plurality of discrete component sheet materials in transport are impregnated with a resin composition and a film is laminated with these resin-treated component sheets as the latter are joined together; or PA1 (2) A plurality of discrete sheet component materials in transport are joined to give an assembly in a resin bath and, thereafter, a film is laminated with the resin-impregnated sheet assembly.
The method described in Japanese Unexamined Patent Publication No. 4838/1980 comprises feeding a plurality of continuous sheet component materials in vertically discrete relation, applying an impregnating resin to said component materials from an overhead resin source, joining the component materials to give an assembly and finally laminating a film with the assembly, all in a continuous sequence. In this production method, where the resin is supplied from an overhead position, the impregnation process takes place only gradually so that it takes a long time for the resin to penetrate into component materials. This time depends on and varies with the type of component materials and the type and viscosity of the resin used but usually ranges from several minutes to scores of minutes. Moreover, to ensure an acceptable finished quality, the plurality of materials are preferably joined after the impregnation has progressed to a sufficient extent. Therefore, a sufficiently long path of travel must be provided between the stage at which the resin composition is applied and the stage where the plurality of discrete resin-impregnated materials are joined to give an assembly. However, if this path of travel is increased, the production equipment must be increased in size. To solve this problem and provide a production method which would not require a large equipment space yet ensure a satisfactory impregnation result, the present inventors conducted an intensive study and found that the above-mentioned objects can be accomplished by feeding a plurality of continuous sheet component materials in vertically discrete relation, supplying an impregnating resin composition to each of said component materials, joining the resin-impregnated component materials into an assembly, laminating a film material onto either side of said assembly, and curing the resulting laminate, all in a continuous sequence, wherein said resin-impregnated sheet component materials are transported in a substantially horizontal path, at least one substantially V-shaped or U-shaped path preceded by a gradually declining path, and an ascending path in the order mentioned before said component materials are joined.
This invention will be described in detail, reference being made to the accompanying drawings.